A PROTEIN, CALLED NEUROPEPTIDE Y (NPY)

A PROTEIN, CALLED NEUROPEPTIDE Y (NPY), that surges into the bloodstream at high levels when people are depressed may be the key to why depression impairs the immune function, says Michael Irwin or the University of California-San Diego Medical School. Earlier studies had showed the link between NPY and decreased infection-fighting cells in a test tube. New findings prove that depressed humans have significantly more NPY in their blood than non-depressed; this correlates with weakened immune activity. Although the link is "a very robust one," Irwin cautions that this doesn't mean that depression will trigger illness in everyone. Older people and those facing stress are the most vulnerable.